diff --git a/Tests/Timer.Tests.ps1 b/Tests/Timer.Tests.ps1
new file mode 100644
index 0000000..24d11b5
--- /dev/null
+++ b/Tests/Timer.Tests.ps1
@@ -0,0 +1,59 @@
+BeforeAll {
+    Import-Module (Join-Path $PSScriptRoot '../IT-ToolBox.psd1') -Force -ErrorAction Stop
+}
+Describe 'Stopwatch lifecycle' {
+    It 'starts, reports status, stops and preserves elapsed time' {
+        $timer=New-Timer
+        $timer | Should -BeOfType ([System.Diagnostics.Stopwatch])
+        Get-TimerStatus $timer | Should -BeTrue
+        [System.Threading.SpinWait]::SpinUntil([Func[bool]]{$timer.ElapsedTicks -gt 0},1000) | Should -BeTrue
+        Stop-Timer $timer | Should -BeTrue
+        Get-TimerStatus $timer | Should -BeFalse
+        $ticks=$timer.ElapsedTicks
+        $ticks | Should -BeGreaterThan 0
+        Stop-Timer $timer | Should -BeTrue
+        $timer.ElapsedTicks | Should -Be $ticks
+        (Get-ElapsedTime -ElapsedTime $timer).Ticks | Should -Be $timer.Elapsed.Ticks
+    }
+    It 'does not start a stopwatch that was never started' {
+        $timer=[System.Diagnostics.Stopwatch]::new()
+        Stop-Timer $timer | Should -BeTrue
+        Get-TimerStatus $timer | Should -BeFalse
+        $timer.ElapsedTicks | Should -Be 0
+    }
+    It 'rejects null and incompatible inputs' {
+        {Stop-Timer -Timer $null} | Should -Throw
+        {Get-TimerStatus -Timer $null} | Should -Throw
+        {Stop-Timer -Timer 'invalid'} | Should -Throw
+        {Get-TimerStatus -Timer 'invalid'} | Should -Throw
+    }
+    It 'preserves caller and module preferences starting with <Preference>' -ForEach @(
+        @{ Preference = 'Continue' }
+        @{ Preference = 'Stop' }
+    ) {
+        $module = Get-Module IT-ToolBox
+        $originalModulePreference = & $module { $script:ErrorActionPreference }
+        $originalCallerPreference = $ErrorActionPreference
+        try {
+            $ErrorActionPreference = $Preference
+            & $module { param($value) $script:ErrorActionPreference = $value } $Preference
+            $timer = New-Timer
+            Stop-Timer $timer | Should -BeTrue
+            $ErrorActionPreference | Should -Be $Preference
+            (& $module { $script:ErrorActionPreference }) | Should -Be $Preference
+            { Stop-Timer -Timer $null } | Should -Throw
+            $ErrorActionPreference | Should -Be $Preference
+            (& $module { $script:ErrorActionPreference }) | Should -Be $Preference
+        }
+        finally {
+            & $module { param($value) $script:ErrorActionPreference = $value } $originalModulePreference
+            $ErrorActionPreference = $originalCallerPreference
+        }
+    }
+    It 'accepts verbose diagnostics and returns a boolean' {
+        $timer=New-Timer
+        $result=Stop-Timer $timer -Verbose
+        $result | Should -BeOfType ([bool])
+        Get-TimerStatus $timer -Verbose | Should -BeFalse
+    }
+}